1. Field of the Invention
Exemplary aspects of the present invention generally relate to a method of measuring the difference between the rotational center of a rotary disk of a rotary encoder and the center of a radial scale provided on the rotary disk to detect an amount of rotational eccentricity, and an image forming apparatus including the rotary encoder.
2. Description of the Background Art
One example of a device that detects a rotational state of a rotary member, in particular such characteristics as rotation speed and amount of rotation thereof (i.e., angle of rotation), is a photoelectric rotary encoder. as rotation speed and amount of rotation thereof (i.e., angle of rotation), is a photoelectric rotary encoder.
In the photoelectric rotary encoder, the periphery of a disk connected to the shaft of the rotary member is provided with a radial scale including alternating light-transmitting portions and light-blocking portions, or light-reflecting portions and light-absorbing portions. A light projector projects a light flux (a light beam) onto the radial scale, and light reflected by or transmitted through the radial scale is detected by a detection device. Then, using signals from the detection device, the rotational state of the rotary disk is identified.
In general, the detection accuracy of the above-described rotary encoder decreases significantly if the center of rotation of the rotary disk and the center of the radial scale are not properly aligned. Obviously, such reduction in detection accuracy can be prevented by properly aligning the center of rotation of the rotary disk and the center of the radial scale, and to accomplish that the accuracy of manufacturing and assembly of the radial scale and the center of rotation of the rotary disk may be enhanced, as in certain known techniques. Alternatively, the radial scale may be attached to the rotary shaft while the center of the rotary disk or the radial scale and the center of rotation of the rotary shaft are adjusted with the use of a microscope or the like, as in other background techniques.
If the accuracy of the manufacturing and assembly of the radial scale and the center of rotation of the rotary disk is increased, adjustment is unnecessary in the assembly or replacement of components, and thus the assembly work is simplified. However, to achieve such relatively high accuracy is expensive. This is because it is difficult to assemble and adjust the rotary disk and the rotary shaft, and thus it takes a relatively long time for the assembly and adjustment.
FIG. 20 is a diagram illustrating an example of post-production measurement of eccentricity of a rotary disk according to a background technique.
A rotary disk 300 illustrated in FIG. 20 includes a mounting portion 301 and a radial scale 302. The mounting portion 301, which is a hole near the center of the rotary disk 300 shown in FIG. 20, is used to attach the rotary disk 300 to a detected object, for example, a rotary member such as a roller.
To calculate the center of rotation c1 of the rotary disk 300, the coordinates of an arbitrary point on the circumference of the mounting portion 301 are first measured at least three locations (for example, three locations in the drawing). On the basis of the measured coordinates, the coordinates of the center of rotation c1 of the rotary disk 300 can be calculated.
Subsequently, to calculate the center c2 of the radial scale 302, the coordinates of an arbitrary point p2 on the circumference of a circle pattern 303 drawn concentrically with the radial scale 302 are measured at least three locations (for example, the three locations in the drawing). On the basis of the measured coordinates, the coordinates of the center c2 of the radial scale 302 can be calculated.
The previously calculated coordinates of the center of rotation c1 of the rotary disk 300 are then compared with the coordinates of the center c2 of the radial scale 302 to obtain an eccentricity amount D, if such is present.
Ultimately, whether or not the obtained eccentricity amount D meets a separately set standard is checked, and whether or not the rotary disk 300 can be used is determined.
With this configuration, the assembly time for the rotary disk can be reduced, and no adjustment tool is necessary even if the rotary disk needs to be replaced when the rotary disk fails. Furthermore, the time for measuring the eccentricity amount can also be reduced.
However, in the above-described eccentricity measurement method, in order to perform accurate measurement, it is necessary to accurately select the respective measurement points p1 and p2 without misalignment. In order to accurately select the measurement points, the expertise of a measurer and complicated image processing by a measuring device are necessary. As a result, the time for completing the measurement is increased.